RESUMO
We report the measurement of degenerate coherent anti-Stokes Raman scattering (CARS) in a high-finesse optical microcavity, with an atmospheric gas as the nonlinear medium. Unlike the well-known bulk process in which index-dispersion compensation is required for phase-matching, efficient microcavity CARS involves a resonant coupling at the Stokes, pump, and anti-Stokes frequencies which can be described using coupled-mode analysis. We show how the interaction is thereby dramatically enhanced in a microscopic sample volume and illustrate the technique for the measurement of CO2 in air.
RESUMO
A novel heat-sinking, self-referencing fiber optic emission probe having a sapphire fiber probe head is described. The laser heating effect in a GaAs wafer (on a polytetrafluoroethylene (PTFE) platform) has been measured with the probe in both the noncontact proximity mode and the contact mode. The GaAs/PTFE composite was selected to simulate the thermal conductivity of animal tissues. It was found that for the same laser power delivered to the wafer, the temperature rise in the contact mode was only 42% of that in the proximity mode. Additionally, a demonstration of the self-referencing capability of the probe is also presented.
RESUMO
The influence of particulates on sapphire fiber evanescent wave absorption by water has been studied. Suspensions containing micro-sized graphite flakes and glassy carbon powder were used. Conventional free-space transmittance measurements of these samples showed strong absorption and scattering, which severely screened the absorption by water. However, the absorption on the water band determined from the evanescent wave interaction was unaffected by the presence of the graphite flakes. These results indicate that fiber-optic evanescent wave chemical sensors may be suitable for process control applications involving turbid reactor streams.